BranchProbabilityInfo.cpp File Reference

#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/ProfDataUtils.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdint>
#include <map>
#include <utility>

Go to the source code of this file.

Macros
#define	DEBUG_TYPE   "branch-prob"

Typedefs
using	ProbabilityList = SmallVector< BranchProbability >
using	ProbabilityTable = std::map< CmpInst::Predicate, ProbabilityList >

Enumerations
enum class	BlockExecWeight : std::uint32_t {   ZERO = 0x0 , LOWEST_NON_ZERO = 0x1 , UNREACHABLE = ZERO , NORETURN = LOWEST_NON_ZERO ,   UNWIND = LOWEST_NON_ZERO , COLD = 0xffff , DEFAULT = 0xfffff }
	Set of dedicated "absolute" execution weights for a block. More...

Functions
	INITIALIZE_PASS_BEGIN (BranchProbabilityInfoWrapperPass, "branch-prob", "Branch Probability Analysis", false, true) INITIALIZE_PASS_END(BranchProbabilityInfoWrapperPass
static const BranchProbability	PtrTakenProb (PH_TAKEN_WEIGHT, PH_TAKEN_WEIGHT+PH_NONTAKEN_WEIGHT)
static const BranchProbability	PtrUntakenProb (PH_NONTAKEN_WEIGHT, PH_TAKEN_WEIGHT+PH_NONTAKEN_WEIGHT)
static const BranchProbability	ZeroTakenProb (ZH_TAKEN_WEIGHT, ZH_TAKEN_WEIGHT+ZH_NONTAKEN_WEIGHT)
static const BranchProbability	ZeroUntakenProb (ZH_NONTAKEN_WEIGHT, ZH_TAKEN_WEIGHT+ZH_NONTAKEN_WEIGHT)
static const BranchProbability	FPOrdTakenProb (FPH_ORD_WEIGHT, FPH_ORD_WEIGHT+FPH_UNO_WEIGHT)
static const BranchProbability	FPOrdUntakenProb (FPH_UNO_WEIGHT, FPH_ORD_WEIGHT+FPH_UNO_WEIGHT)
static const BranchProbability	FPTakenProb (FPH_TAKEN_WEIGHT, FPH_TAKEN_WEIGHT+FPH_NONTAKEN_WEIGHT)
static const BranchProbability	FPUntakenProb (FPH_NONTAKEN_WEIGHT, FPH_TAKEN_WEIGHT+FPH_NONTAKEN_WEIGHT)
static void	computeUnlikelySuccessors (const BasicBlock *BB, Loop *L, SmallPtrSetImpl< const BasicBlock * > &UnlikelyBlocks)

Variables
static cl::opt< bool >	PrintBranchProb ("print-bpi", cl::init(false), cl::Hidden, cl::desc("Print the branch probability info."))
cl::opt< std::string >	PrintBranchProbFuncName ("print-bpi-func-name", cl::Hidden, cl::desc("The option to specify the name of the function " "whose branch probability info is printed."))
branch	prob
branch Branch Probability	Analysis
branch Branch Probability	false
static const uint32_t	LBH_TAKEN_WEIGHT = 124
static const uint32_t	LBH_NONTAKEN_WEIGHT = 4
static const BranchProbability	UR_TAKEN_PROB = BranchProbability::getRaw(1)
	Unreachable-terminating branch taken probability.
static const uint32_t	PH_TAKEN_WEIGHT = 20
	Heuristics and lookup tables for non-loop branches: Pointer Heuristics (PH)
static const uint32_t	PH_NONTAKEN_WEIGHT = 12
static const ProbabilityTable	PointerTable
	Pointer comparisons:
static const uint32_t	ZH_TAKEN_WEIGHT = 20
	Zero Heuristics (ZH)
static const uint32_t	ZH_NONTAKEN_WEIGHT = 12
static const ProbabilityTable	ICmpWithZeroTable
	Integer compares with 0:
static const ProbabilityTable	ICmpWithMinusOneTable
	Integer compares with -1:
static const ProbabilityTable	ICmpWithOneTable
	Integer compares with 1:
static const ProbabilityTable	ICmpWithLibCallTable
	strcmp and similar functions return zero, negative, or positive, if the first string is equal, less, or greater than the second.
static const uint32_t	FPH_TAKEN_WEIGHT = 20
static const uint32_t	FPH_NONTAKEN_WEIGHT = 12
static const uint32_t	FPH_ORD_WEIGHT = 1024 * 1024 - 1
	This is the probability for an ordered floating point comparison.
static const uint32_t	FPH_UNO_WEIGHT = 1
	This is the probability for an unordered floating point comparison, it means one or two of the operands are NaN.
static const ProbabilityTable	FCmpTable
	Floating-Point compares:

Macro Definition Documentation

DEBUG_TYPE

#define DEBUG_TYPE   "branch-prob"

Definition at line 51 of file BranchProbabilityInfo.cpp.

Typedef Documentation

ProbabilityList

using ProbabilityList = SmallVector<BranchProbability>

Definition at line 118 of file BranchProbabilityInfo.cpp.

ProbabilityTable

using ProbabilityTable = std::map<CmpInst::Predicate, ProbabilityList>

Definition at line 119 of file BranchProbabilityInfo.cpp.

Enumeration Type Documentation

BlockExecWeight

enum class BlockExecWeight : std::uint32_t

strong

Set of dedicated "absolute" execution weights for a block.

These weights are meaningful relative to each other and their derivatives only.

Enumerator
ZERO	Special weight used for cases with exact zero probability.
LOWEST_NON_ZERO	Minimal possible non zero weight.
UNREACHABLE	Weight to an 'unreachable' block.
NORETURN	Weight to a block containing non returning call.
UNWIND	Weight to 'unwind' block of an invoke instruction.
COLD	Weight to a 'cold' block. Cold blocks are the ones containing calls marked with attribute 'cold'.
DEFAULT	Default weight is used in cases when there is no dedicated execution weight set. It is not propagated through the domination line either.

Definition at line 197 of file BranchProbabilityInfo.cpp.

Function Documentation

computeUnlikelySuccessors()

static void computeUnlikelySuccessors ( const BasicBlock *  BB, Loop *  L, SmallPtrSetImpl< const BasicBlock * > &  UnlikelyBlocks  )

static

Definition at line 542 of file BranchProbabilityInfo.cpp.

References B, llvm::ConstantFoldBinaryOpOperands(), llvm::ConstantFoldCompareInstOperands(), DL, llvm::SmallVectorBase< Size_T >::empty(), llvm::BranchInst::getCondition(), llvm::BasicBlock::getDataLayout(), llvm::User::getOperand(), llvm::CmpInst::getPredicate(), llvm::BranchInst::getSuccessor(), llvm::BasicBlock::getTerminator(), I, llvm::SmallPtrSetImpl< PtrType >::insert(), llvm::is_contained(), llvm::BranchInst::isConditional(), P, llvm::SmallVectorImpl< T >::pop_back_val(), llvm::SmallVectorTemplateBase< T, bool >::push_back(), llvm::reverse(), and llvm::successors().

FPOrdTakenProb()

static const BranchProbability FPOrdTakenProb ( FPH_ORD_WEIGHT  , FPH_ORD_WEIGHT+  FPH_UNO_WEIGHT  )

static

FPOrdUntakenProb()

static const BranchProbability FPOrdUntakenProb ( FPH_UNO_WEIGHT  , FPH_ORD_WEIGHT+  FPH_UNO_WEIGHT  )

static

FPTakenProb()

static const BranchProbability FPTakenProb ( FPH_TAKEN_WEIGHT  , FPH_TAKEN_WEIGHT+  FPH_NONTAKEN_WEIGHT  )

static

FPUntakenProb()

static const BranchProbability FPUntakenProb ( FPH_NONTAKEN_WEIGHT  , FPH_TAKEN_WEIGHT+  FPH_NONTAKEN_WEIGHT  )

static

INITIALIZE_PASS_BEGIN()

INITIALIZE_PASS_BEGIN	(	BranchProbabilityInfoWrapperPass	,
		"branch-prob"	,
		"Branch Probability Analysis"	,
		false	,
		true
	)

PtrTakenProb()

static const BranchProbability PtrTakenProb ( PH_TAKEN_WEIGHT  , PH_TAKEN_WEIGHT+  PH_NONTAKEN_WEIGHT  )

static

PtrUntakenProb()

static const BranchProbability PtrUntakenProb ( PH_NONTAKEN_WEIGHT  , PH_TAKEN_WEIGHT+  PH_NONTAKEN_WEIGHT  )

static

ZeroTakenProb()

static const BranchProbability ZeroTakenProb ( ZH_TAKEN_WEIGHT  , ZH_TAKEN_WEIGHT+  ZH_NONTAKEN_WEIGHT  )

static

ZeroUntakenProb()

static const BranchProbability ZeroUntakenProb ( ZH_NONTAKEN_WEIGHT  , ZH_TAKEN_WEIGHT+  ZH_NONTAKEN_WEIGHT  )

static

Variable Documentation

Analysis

branch Branch Probability Analysis

Definition at line 69 of file BranchProbabilityInfo.cpp.

false

branch Branch Probability false

Definition at line 69 of file BranchProbabilityInfo.cpp.

FCmpTable

const ProbabilityTable FCmpTable

static

Initial value:

{
    {FCmpInst::FCMP_ORD, {FPOrdTakenProb, FPOrdUntakenProb}}, 
    {FCmpInst::FCMP_UNO, {FPOrdUntakenProb, FPOrdTakenProb}}, 
}

Floating-Point compares:

Definition at line 190 of file BranchProbabilityInfo.cpp.

FPH_NONTAKEN_WEIGHT

const uint32_t FPH_NONTAKEN_WEIGHT = 12

static

Definition at line 171 of file BranchProbabilityInfo.cpp.

FPH_ORD_WEIGHT

const uint32_t FPH_ORD_WEIGHT = 1024 * 1024 - 1

static

This is the probability for an ordered floating point comparison.

Definition at line 174 of file BranchProbabilityInfo.cpp.

FPH_TAKEN_WEIGHT

const uint32_t FPH_TAKEN_WEIGHT = 20

static

Definition at line 170 of file BranchProbabilityInfo.cpp.

FPH_UNO_WEIGHT

const uint32_t FPH_UNO_WEIGHT = 1

static

This is the probability for an unordered floating point comparison, it means one or two of the operands are NaN.

Usually it is used to test for an exceptional case, so the result is unlikely.

Definition at line 178 of file BranchProbabilityInfo.cpp.

ICmpWithLibCallTable

const ProbabilityTable ICmpWithLibCallTable

static

Initial value:

{
    {CmpInst::ICMP_EQ, {ZeroUntakenProb, ZeroTakenProb}},
    {CmpInst::ICMP_NE, {ZeroTakenProb, ZeroUntakenProb}},
}

strcmp and similar functions return zero, negative, or positive, if the first string is equal, less, or greater than the second.

We consider it likely that the strings are not equal, so a comparison with zero is probably false, but also a comparison with any other number is also probably false given that what exactly is returned for nonzero values is not specified. Any kind of comparison other than equality we know nothing about.

Definition at line 164 of file BranchProbabilityInfo.cpp.

ICmpWithMinusOneTable

const ProbabilityTable ICmpWithMinusOneTable

static

Initial value:

{
    {CmpInst::ICMP_EQ, {ZeroUntakenProb, ZeroTakenProb}},  
    {CmpInst::ICMP_NE, {ZeroTakenProb, ZeroUntakenProb}},  
    
    {CmpInst::ICMP_SGT, {ZeroTakenProb, ZeroUntakenProb}}, 
}

Integer compares with -1:

Definition at line 144 of file BranchProbabilityInfo.cpp.

ICmpWithOneTable

const ProbabilityTable ICmpWithOneTable

static

Initial value:

{
    
    {CmpInst::ICMP_SLT, {ZeroUntakenProb, ZeroTakenProb}}, 
}

Integer compares with 1:

Definition at line 152 of file BranchProbabilityInfo.cpp.

ICmpWithZeroTable

const ProbabilityTable ICmpWithZeroTable

static

Initial value:

{
    {CmpInst::ICMP_EQ, {ZeroUntakenProb, ZeroTakenProb}},  
    {CmpInst::ICMP_NE, {ZeroTakenProb, ZeroUntakenProb}},  
    {CmpInst::ICMP_SLT, {ZeroUntakenProb, ZeroTakenProb}}, 
    {CmpInst::ICMP_SGT, {ZeroTakenProb, ZeroUntakenProb}}, 
}

Integer compares with 0:

Definition at line 136 of file BranchProbabilityInfo.cpp.

LBH_NONTAKEN_WEIGHT

const uint32_t LBH_NONTAKEN_WEIGHT = 4

static

Definition at line 100 of file BranchProbabilityInfo.cpp.

LBH_TAKEN_WEIGHT

const uint32_t LBH_TAKEN_WEIGHT = 124

static

Definition at line 99 of file BranchProbabilityInfo.cpp.

PH_NONTAKEN_WEIGHT

const uint32_t PH_NONTAKEN_WEIGHT = 12

static

Definition at line 112 of file BranchProbabilityInfo.cpp.

PH_TAKEN_WEIGHT

const uint32_t PH_TAKEN_WEIGHT = 20

static

Heuristics and lookup tables for non-loop branches: Pointer Heuristics (PH)

Definition at line 111 of file BranchProbabilityInfo.cpp.

PointerTable

const ProbabilityTable PointerTable

static

Initial value:

{
    {ICmpInst::ICMP_NE, {PtrTakenProb, PtrUntakenProb}}, 
    {ICmpInst::ICMP_EQ, {PtrUntakenProb, PtrTakenProb}}, 
}

Pointer comparisons:

Definition at line 122 of file BranchProbabilityInfo.cpp.

PrintBranchProb

cl::opt< bool > PrintBranchProb("print-bpi", cl::init(false), cl::Hidden, cl::desc("Print the branch probability info.")) ( "print-bpi"  , cl::init(false)  , cl::Hidden  , cl::desc("Print the branch probability info.")    )

static

Referenced by llvm::BranchProbabilityInfo::calculate().

PrintBranchProbFuncName

cl::opt< std::string > PrintBranchProbFuncName("print-bpi-func-name", cl::Hidden, cl::desc("The option to specify the name of the function " "whose branch probability info is printed."))	(	"print-bpi-func-name"	,
		cl::Hidden	,
		cl::desc("The option to specify the name of the function " "whose branch probability info is printed.")
	)

Referenced by llvm::BranchProbabilityInfo::calculate().

prob

branch prob

Definition at line 68 of file BranchProbabilityInfo.cpp.

UR_TAKEN_PROB

const BranchProbability UR_TAKEN_PROB = BranchProbability::getRaw(1)

static

Unreachable-terminating branch taken probability.

This is the probability for a branch being taken to a block that terminates (eventually) in unreachable. These are predicted as unlikely as possible. All reachable probability will proportionally share the remaining part.

Definition at line 107 of file BranchProbabilityInfo.cpp.

ZH_NONTAKEN_WEIGHT

const uint32_t ZH_NONTAKEN_WEIGHT = 12

static

Definition at line 129 of file BranchProbabilityInfo.cpp.

ZH_TAKEN_WEIGHT

const uint32_t ZH_TAKEN_WEIGHT = 20

static

Zero Heuristics (ZH)

Definition at line 128 of file BranchProbabilityInfo.cpp.